Trish, already spoke with you over chat, so I'll reiterate for anyone else interested.
Doggy is not itchy, no irritation, no licking, no hairloss, no change in diet, environment, or stressful situations. Pigment changes are darkening on the chest and legs directly on the skin, not the fur.
First thought is, probably not a big deal, if pigmenting is not super dark, would consider aging, or pigmenting changes due to stress on the body or hormonal changes. Have vet take a look, might want to run bloodwork if anything on physical exam besides skin is abnormal.
Also consider mild demodex even if itchiness isn't there, but if skin scrape is negative...
Possibly early signs of melanoma? Highly doubtful, requires skin biopsy to test.
Make sure you have your vet check to rule out anything it could possibly be, please update us and let us know how your pup is doing.